Conversion of hydrocarbons



Patented May 10,- 1938 UNITED STATES PATENT OFFICE 2,116,773 CONVERSION or nrnaocarinons Vanderveer Voorhees,

Hammond, I nd., assignor to Standard Oil Company (Indiana), Chicago, 11]., a corporation of Indiana No Drawing.

Application November 21, 1934, Serial No. 754,089

1 Claim. (01. zoo-rim This invention relates to the conversion of hydrocarbons and pertains particularly to a method of treating the hydrocarbons so as to improve the overall efficiency of the operation and, reduce or inhibit the formation of carbon The reduction of saturated hydrocarbon gases to unsaturated hydrocarbon gases by pyrolytic treatment, as outlined above, even under care.- iully controlled conditions, usually results in the formation of carbon and carbon deposits within the heating tubes, which shortens the operating period for the equipment. 2 I have found that the presence of oxygen and oxygen containing compounds even in small quantities, within the gases being treated tends to accelerate the formation of carbon and carbon deposition within the heating tubes reduces the yield and otherwise reduces the overall efli-. ciency of the process. phenomena is not definitely known, it may. be due to a negative catalytic effect exerted bythe oxygen itself, or the oxygen in combination with other constituents of thegas or in combination with the metal walls of the equipment, which suppresses the desired reactions and accelerates undesirable reactions resulting in the formation of carbon. Whatever the explanation maybe, 40 the presence of oxygen and oxygen containing compounds does reduce the efficiency of treatment.

In accordance with my invention, the hydro carbons to be subjected to p'yrolytic treatment as 45 hereinbefore described, are first treated to remove oxygen and oxygen containing compounds therefrom. f

The free oxygen may be removed from the gases by any one of a number of generally 50' known deoxidizing methods. For example, the gases may be heated to a moderate temperature, for example, in the neighborhood of 300 to 400 F. and then passed over powdered aluminum, or they may be heated to a higher temperature 6 such as from 700 to 800 F., and then treated While the reason for this with powdered zinc, after which the unoxidized zinc and the zinc oxide may be removed by precipitation in any des'iredmanner. As a further" example, the gases may be heated to a temperature in the neighborhood of 1300 F. and then 5 passed through a bed of sponge iron or iron filings. In the latter case, it is preferred to pass the gases promptly to the gas pyrolysis zone for immediate conversion into unsaturated constituents. Moreover, it is also desirable in the latter 10 case to pass the gases. over the sponge iron rapidly in order-to prevent any" substantial conversion of the gases during the deoxidizing treatment.

The above examples are given merely for purposes of illustration, for as above pointed out this deoxidation may be accomplished by any one of a number of generally known methods.

The'nature of treatment of the gases to remove the oxygen containing compounds will depend upon the nature of these compounds, which in turn will depend largely upon the origin and source of gases to be treated. For example, hydrocarbon gases resulting from the distillation and cracking treatment of petroleum oils will 5 usually contain free oxygen, water vapor, carbon monoxide and carbon dioxide. A

'When treating gases of this character, it is preferred to first remove the oxygen containing compounds before removing the free oxygen. I

For example, the gases may be first passed through a bed of calcium oxide or quick lime to remove the moisture and carbon dioxide. The gases may, however, be treated by any other dehydrating agent, such as calcium chloride, sulphuric acid, metallic sodium and many other agents. a

After removing the oxygen-containing compounds the gas is then treated to remove the free oxygen therefrom in any convenient manner, as hereinbefore described.

The following specific example will aid me better understanding of the invention.

Gases resulting from the refining of hydrocarbon'oils (for example gases from the top of a stabilizer, used for stabilizing natural gasoline) may be first passed through a bed of quick lime (calcium oxide) for removal of water vapor and carbon dioxide. The gases may thereafter be treated with zinc vapors at a temperature in the neighborhood of 800 F. to remove the free oxygen. The gases may then be cooled to condense the unoxi'dized zinc andthe zin'c oxide formed during the treatment and the unoxidized zinc and zinc oxide precipitated or filtered from the gases in any desired manner.

The gases after being treated to remove the oxygen and oxygen containing compounds may be thereafter subjected to pyrolytic conversion treatment. For example, the gases may be heated to a temperature ranging from 1,000 to 1700 F., while passing at a relatively high velocity through a plurality of heating tubes mounted within the furnace. The pressure maintained may vary greatly depending on the type of prod-- uct desired. For example, the use of low pressures from to 200 lbs. per square inch will produce a higher proportion of olefines and unsaturated hydrocarbons such as ethylene, propylene, cyclopentene, etc., whereas higher pressures of from 200-3000 lbs. per square inch yield the saturated and aromatic hydrocarbons.

The gases may be subjected to the heat treatment for a relatively short period of time, for example; from a fraction of a second to a few seconds, for the purpose of converting the saturated hydrocarbons into unsaturated end products, or the gases may be subjected to a. longer heat treatment for converting the saturated hydrocarbons into liquid end products of aromatic character. In the latter case, the temperature of conversion may be maintained somewhat higher than when it is desired to produce unsaturated hydrocarbons as end products. In carrying out the process it is preferred to employ heating tubes which are devoid of oxide and scale, which may beobtained by cleaning the furnace tubes with sulfuric or hydrochloric acid inhibited against corrosion attack by a suitable inhibitor such as quinoline, diphenyl and thio urea, etc.

It is also preferable to employ tubes made of .tures wherein the oil phase.

cent chromium, 18 percent chromium and 8 percent nickel maybe employed for this purpose. While I have described the invention in connection with the pyrolysis of low molecular weight hydrocarbon gases, it will also be of advantage in the pyrolytic cracking of higher molecular weight hydrocarbon oils into hydrocarbons of lower molecular weight and particularly in cracking processes involving high cracking temperais cracked in the vapor Having thus described the preferred embodiment, it is understood that my invention embraces such other modifications and variations as come within the scope and spirit thereof, and that it is not my intention to dedicate any novel features of my invention, or to unnecessarily limit the invention, except as necessary to distinguish over the prior art.

I claim:

In the pyrolysis of normally gaseous saturated hydrocarbon vapors, separated from free oxygen and oxygen-containing compounds, into unsatuated gases; the improvement which comprises passing the saturated hydrocarbon gases through a bed of calcium oxide, thereafter heating the gases to a temperature in the neighborhood of 800 F., adding zinc vapors to said gases while at said elevated temperature, thereafter removing the unoxidized zinc and zinc oxide from said hydrocarbon vapors before subjecting the same to the pyrolytic treatment.

VANDERVEER VOORHEES. 

